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601.
602.
Previous measurements from cool microtidal temperate areas suggest that microphytobenthic incorporation of nitrogen (N) exceeds
N removal by denitrification in illuminated shallow-water sediments. The present study investigates if this is true also for
fully nontidal sediments in the Baltic Sea., Sediment-water fluxes of inorganic (DIN) and, organic nitrogen (DON) and oxygen,
as well as denitrification, were measured in early autumn and spring, in light and dark, at four sites representing different
sediment types. All sediments were autotrophic during the daytime both in the autumn and spring. On a 24-h time scale, they
were autotrophic in the spring and heterotrophic in early autumn. Sediments funcitoned as sources of DIN and DON during the
autumn and sinks during the spring, with DON fluxes dominating or being as important as DIN fluxes. Microphytobenthos (MPB)
activity controlled fluxes of both DIN and DON. Significant differences between sites were found, although sediment type (sand
or silt) had no consistent effect on the magnitude of MPB production or nutrient fluxes. The clearest effect related to sediment
type was found for denitrification, although only in the autumn, with higher rates in silty sediments. Estimated N assimilation
by MPB, based on both net primary production (0.7–6.5 mmol N m−2 d−1) and on 80% of gross primary production (1.9–9.4 mmol N m−2 d−1) far exceeded measured rates of denitrification (0.01–0.16 mmol N m−2 d−1). A theoretical calculation showed that MPB may incorporate between 40% and 100% of the remineralized N, while denitrification
removes, <5%. MPB assimilation of N appears to be a far more important N consuming process than denitrification in these nontidal,
shallow-water sediments. 相似文献
603.
Heather Xiaoquan Zhang P. Mick Kelly Catherine Locke Alexandra Winkels W. Neil Adger 《Geoforum》2006,37(6):1066-1081
Migration is frequently portrayed as a negative force in its relationship with economic and social development. This negative perception is exhibited through describing population movements as either ‘forced’ (e.g. political and environmental refugees) or ‘voluntary’ movements (e.g. economic and uninhibited relocation). This paper examines the limitations of this conceptual dualism. It points out that the dualistic approach, widely used in the context of developing countries, simplifies a highly complex phenomenon by ignoring its essential heterogeneity and spatial and temporal dynamics. As such, it is limited in explaining and understanding the globally diversified, historically and politically contextualised situations. Focusing on the migratory experiences of contemporary Vietnam, the study identifies major patterns and trends of population mobility in the country in the past fifty years. It shows that despite the state’s continued attempts to reshape the spatial distribution of population over recent historical periods, the policy outcomes with respect to population mobility have been swayed as much by individuals and their families in pursuit of their own aspirations and livelihoods as by state plans. The Vietnam case has provided evidence of a much more complicated relationship between migration and livelihoods than the conceptual dichotomy assumes, and the opportunity for a richer set of policy options. We argue that the evidence from Vietnam, and elsewhere, warrants an integrated approach to studying migration, combining analysis at the macro- and micro-levels with the nexus lying at the critical decision-making point of the individual or household. 相似文献
604.
605.
Manuel Valera Zhengyang Guo Priscilla Kelly Sean Matz Vito Adrian Cantu Allon G. Percus Jeffrey D. Hyman Gowri Srinivasan Hari S. Viswanathan 《Computational Geosciences》2018,22(3):695-710
Structural and topological information play a key role in modeling flow and transport through fractured rock in the subsurface. Discrete fracture network (DFN) computational suites such as dfnWorks (Hyman et al. Comput. Geosci. 84, 10–19 2015) are designed to simulate flow and transport in such porous media. Flow and transport calculations reveal that a small backbone of fractures exists, where most flow and transport occurs. Restricting the flowing fracture network to this backbone provides a significant reduction in the network’s effective size. However, the particle-tracking simulations needed to determine this reduction are computationally intensive. Such methods may be impractical for large systems or for robust uncertainty quantification of fracture networks, where thousands of forward simulations are needed to bound system behavior. In this paper, we develop an alternative network reduction approach to characterizing transport in DFNs, by combining graph theoretical and machine learning methods. We consider a graph representation where nodes signify fractures and edges denote their intersections. Using random forest and support vector machines, we rapidly identify a subnetwork that captures the flow patterns of the full DFN, based primarily on node centrality features in the graph. Our supervised learning techniques train on particle-tracking backbone paths found by dfnWorks, but run in negligible time compared to those simulations. We find that our predictions can reduce the network to approximately 20% of its original size, while still generating breakthrough curves consistent with those of the original network. 相似文献
606.
Gradon Diprose Kelly Dombroski Emma Sharp Amanda Yates Bailey Peryman Martine Barnes 《New Zealand geographer》2023,79(1):15-26
Aotearoa New Zealand is at a critical juncture in reducing and managing organic waste. Research has highlighted the significant proportion of organic waste sent to landfills and associated adverse effects such as greenhouse gas emissions and loss of valuable organic matter. There is current debate about what practices and infrastructure to invest in to better manage and use organic waste. We highlight the diversity of existing organic waste practices and infrastructures, focusing on Auckland, Wellington and Christchurch. We show how debates about organic waste practices and infrastructure connect across three themes: waste subjectivities, collective action in place and language. 相似文献
607.
The dissimilarity of temperature and humidity transfer in the marine surface layer (MSL) is investigated through the relative transport efficiency and correlation coefficient of these two scalars. We examine their variability and relationship with mean values, as well as spectral characteristics. It is shown that the dissimilarity between these two scalars in the MSL is a function of stability, the boundary-layer depth, and flow steadiness. In general the temperature and humidity are less correlated in shallow marine boundary layers compared to deep marine boundary layers, due to the stronger impact of the boundary-layer scale in breaking the “same source, same sink” assumption for scalar similarity. This is supported by the combination of our spectral analysis of scalar fluxes and corresponding measured and modelled boundary-layer depth. This assumption is also broken in near-neutral conditions, when there is an efficient latent heat transfer but negligible sensible heat transfer. Our data suggest that parametrization of humidity fluxes via similarity theory could still be reliable when the correlation coefficient $>$ 0.5, and in near-neutral conditions the humidity flux can be estimated without use of the sensible heat flux. 相似文献
608.
Static flux chamber measurements of CCl4 uptake by soils in boreal, subtropical and tropical forests have been used to reassess the sink strength for this ozone depleting chemical. Happell and Roche (Geophys. Res. Lett. 30(2), 1088–1091, 2003) used flux estimates from soil concentration gradients to calculate a partial CCl4 atmospheric lifetime (τsoil) of 90 years. More recently, it is has been assumed that a better estimate of τsoil is 195 years (Montzka et al. 2011). In the work here, the rate of CCl4 uptake was calculated from 453 flux chamber measurements using an exponential fit to the chamber CCl4 concentration change with time. This analysis indicated that the flux rate estimate in Happell and Roche (Geophys. Res. Lett. 30(2) 1088–1091, 2003) was overestimated by 2.75, yielding a new estimate of τsoil for CCl4 of 245 years. Significant correlations of CCl4 uptake to temperature, soil moisture, or time of year were not observed. This work provides additional evidence that CCl4 uptake by soils is a common process and needs to be considered when developing an atmospheric budget for this compound. 相似文献
609.
Bronfenbrenner’s bioecological theory for modelling community resilience to natural disasters 总被引:1,自引:1,他引:0
Helen J. Boon Alison Cottrell David King Robert B. Stevenson Joanne Millar 《Natural Hazards》2012,60(2):381-408
This paper advocates the use of Bronfenbrenner’s bioecological theory as a framework to analyse resilience at diverse scales. Bronfenbrenner’s bioecological theory can be employed to (a) benchmark
social resilience, (b) target the priority interventions required and (c) measure progress arising from these interventions
to enhance resilience to natural disasters. First, the paper explores resilience to natural disasters in the context of climatic
change as building resilience is seen as a way to mitigate impacts of natural disasters. Second, concepts of resilience are
systematically examined and documented, outlining resilience as a trait and resilience as a process. Third, issues arising
in relation to the measurement of resilience are discussed. Fourth, Bronfenbrenner’s bioecological systems theory is described
and proffered to model and assess resilience at different scales. Fifth, studies are described which have supported the use
of the bioecological systems theory for the study of resilience. Sixth, an example of the use of Bronfenbrenner’s theory is
offered and the paper concludes with suggestions for future research using Bronfenbrenner’s theory. 相似文献
610.
Joel C. Hoffman Gregory S. Peterson Anne M. Cotter John R. Kelly 《Estuaries and Coasts》2010,33(6):1391-1405
We characterized stable isotope mixing along a river-Great Lake transition zone in the St. Louis River, an important fish
nursery in western Lake Superior, and used it to identify food web linkages supporting young fish production. We observed
a broad, spatial pattern in the carbon stable isotope ratio (δ13C); downriver enrichment in particulate organic carbon and aquatic vegetation δ13C, as well as pelagic, benthic and littoral invertebrate δ13C, reflected isotope mixing along the river-lake transition zone. Fishes with similarly enriched δ13C were used to identify benthopelagic and littoral trophic pathways. River and Lake Superior organic matter (OM) sources contributed
to both pathways. Differences between the δ13C in fishes and invertebrate prey revealed that fish production was supported at multiple spatial scales. The result was that
the food web specific to any location along the transition zone incorporated multiple OM sources from across the watershed. 相似文献